1. Field of the Invention
The invention relates to a forced induction device for a combustion engine, a combustion engine with such a forced induction device and a method for operating a combustion engine that has a forced induction device.
2. Description of the Related Art
Exhaust turbocharging requires a rapid response by the exhaust turbocharger. An exhaust turbocharger that is too small ensures a rapid response, but can make available fresh air or combustion air to the combustion engine to only a limited extent in the upper speed and/or load range. A large exhaust turbocharger can make available sufficient combustion air, but has a poor response due to a high mass moment of inertia of its rotor assembly.
A combination of two exhaust turbochargers often is used in the construction of combustion engines. Various arrangements of the exhaust turbochargers relative to one another and positioning of the various control elements at different branches and entries of a duct system are provided for fluidically connecting the two exhaust turbochargers to one another. In particular, the aim is to combine two traditional forced induction methods, sequential charging and 2-stage charging, in such a way that a desired operating behavior of the combustion engine can be achieved.
DE 10 2011 008 566,DE 10 2011 107 120 and EP 2 402 576 and EP 1 519 017 disclose forced induction devices having two exhaust turbochargers arranged in series. The turbines of the exhaust turbochargers are arranged in an exhaust line of the combustion engine and the compressors are arranged in an intake section of the combustion engine to implement single, parallel or serial operation of the two exhaust turbochargers in different operating ranges of the combustion engine. The exhaust line has a single exhaust manifold that is connected fluidically to the combustion engine in such a way that all of the outlet ports of the combustion engine are connected to the exhaust manifold in a manner that allows through flow. Thus, exhaust gas from the individual cylinder head or the individual outlet ports first flows through this single exhaust manifold before it flows through the turbines into the exhaust line in accordance with a valve configuration.
DE 10 2008 036 308 discloses a combustion engine having first and second exhaust turbochargers. First and second outlet ports of the cylinder head are formed per cylinder head of the combustion engine. The first exhaust turbocharger is connected to the first outlet ports in a manner that allows through flow and the second exhaust turbocharger is connected to the second outlet ports in a manner that allows through flow. A selector valve enables exhaust gas flowing through the second outlet ports to be admitted to the first exhaust turbocharger. A variable valve timing system also is provided for changing a timing of the outlet valves and modifying a corresponding time of admission to the corresponding turbine. An exhaust turbocharger that is bypassed no longer has a flow therethrough, and its rotor assembly comes to a halt. Therefore, the mass moment of inertia must be overcome when exhaust gas is re-admitted to the exhaust turbocharger and impacts the stationary rotor. This leads to a delayed response.
EP 1 400 667 discloses a forced induction device for a combustion engine with first and second outlet ports at each cylinder head. The first outlet ports connect to a first exhaust turbocharger in a manner that allows through flow and the second outlet ports connect to a second exhaust turbocharger in a manner that allows through flow. A valve timing system connects fluidically to the second exhaust turbocharger for shutting down outlet valves. However, this forced induction device does not permit the two exhaust turbochargers to be operated independently of one another in a sequential charging mode, and hence the two exhaust turbochargers are not used efficiently.
It is an object of the invention to provide a forced induction device that can be operated efficiently. It is another object of the invention to develop a combustion engine that has an improved response while simultaneously having a high power. A further object of the invention to specify a method for operating a combustion engine efficiently.